The field of the invention is radio frequency resonators, and particularly, resonators employed in gyromagnetic resonance spectroscopy.
Gyromagnetic resonance spectroscopy is conducted to study nuclei that have a magnetic moment, which is called nuclear magnetic resonance (NMR) and electrons which are in a paramagnetic state which is called paramagnetic resonance (EPR) or electron spin resonance (ESR). There are also a number of other forms of gyromagnetic spectroscopy that are practiced less frequently, but are also included in the field of this invention. In gyromagnetic resonance spectroscopy a sample to be investigated is subjected to a polarizing magnetic field and one or more radio frequency magnetic fields. The frequency, strength, direction, and modulation of the magnetic fields varies considerably depending upon the phenomena being studied. Apparatus such as that disclosed in U.S. Pat. Nos. 3,358,222 and 3,559,043 has been employed for performing such experiments in laboratories, but widespread commercial use of gyromagnetic resonance spectroscopy techniques has been limited.
The reason for the limited commercial application of gyromagnetic resonance spectrometers is their complexity and high cost. Very high radio frequencies are required for some measurement techniques (such as electron spin resonance measurements) and very strong polarizing magnetic fields are required for others (such as nuclear magnetic resonance). In addition, the physical structures for applying multiple fields to a specimen are complex particularly when the temperature of the specimen is to be controlled, or the specimen is to be irradiated with light during the measurement.
A loop-gap resonator which offers many advantages over prior structures used in gyromagnetic resonance spectrometers is disclosed in our co-pending U.S. patent application Ser. No. 310,231 which was filed on Oct. 9, 1981, now U.S. Pat. No. 4,446,429, and which is entitled "Microwave Resonator". The size of this loop-gap resonator, the number and size of the gaps which it contains and the materials from which it is constructed are variables which enable the resonator to be used in a wide variety of measurements and over a wide range of frequencies.
This loop-gap resonator employs a shield which not only confines the electric and magnetic fields to the resonator but which also increases the quality factor, or Q, of the resonator. The resulting structure is generally cylindrical and is convenient for many gyromagnetic resonance measurements. On the other hand, the shield is a separate element which adds complexity and cost to the resonator structure. To provide adequate thermal and mechanical stability the separate elements must be mounted firmly together using structures such as those disclosed in our co-pending U.S. patent application Ser. No. 361,594 which was filed on Mar. 25, 1982, now U.S. Pat. No. 4,453,147, and which is entitled "Modular Lumped Circuit Resonator". The difficulty of providing mechanical stability increases as the number of gaps in the resonator are increased and at microwave frequencies the dimensions of the separate parts are less than one millimeter making machining and assembly of these prior structures difficult.